The long-term objective of this research is to understand how synaptic processing in auditory cortex transforms the neural representation of temporally structured sounds such as music and speech. The focus in this proposal is to test specific hypotheses about how synaptic inhibition transforms the representation of sound from a temporal code into a rate code. This transformation may support multi-sensory integration, because information from sensory areas with different dynamics may need to be converted into a common rate code to be meaningfully combined. The synaptic mechanisms underlying this process remain unknown. Aim 1 will test whether sustained rate-coded responses in auditory cortex are generated by a stimulus-specific decrease in synaptic inhibition. Aim 2 will test whether rate-coded responses to periodic stimuli are generated by a stimulus-specific decrease in synaptic inhibition. Aim 3 will test whether opponent processing of periodic stimuli occurs by a synaptic push-pull mechanism. To accomplish these aims, we will use whole-cell voltage clamp recordings from rat auditory cortical neurons to measure the excitation and inhibition evoked by optimal tones and periodic stimuli. These experiments will help to elucidate the synaptic mechanisms that transform how temporally structured sounds are encoded in auditory cortex. Because temporal structure provides information critical for speech perception, the synaptic processing of time-varying signals in auditory cortex is especially relevant to our understanding of the mechanisms underlying speech processing. The proposed studies will therefore contribute to our basic understanding of the cortical synaptic mechanisms involved in speech perception.